swift - 在Firebase中将观察转换为observeSingleEvent时出错

我现在有一个观察手柄，可以在添加新频道时进行检查。我希望它是一个带有按钮的observesingleevent，当用户单击它时，该按钮将重新加载频道。ObserveSingleEvent工作正常。这是代码：

private func observeChannels() {
    channelRefHandle = channelRef.observe(.childAdded, with: { (snapshot) -> Void in
        self.playersInChannnel.append("\(snapshot.childrenCount)")
        let channelData = snapshot.value as! Dictionary<String, AnyObject>
        let id = snapshot.key
        if let name = channelData["name"] as! String!, name.characters.count > 0 {
            self.channels.append(Channel(id: id, name: name))
            self.tableView.reloadData()
        } else {
            print("Error! Could not decode channel data")
        }
    })
}

我现在试着把它转换成observesingleevent，把打印出来的都说是错误的，无法解码通道数据。这是我的代码：

func reloadChannels()
{
    channelRef.observeSingleEvent(of: .value, with: { (snapshot) -> Void in
        self.playersInChannnel.append("\(snapshot.childrenCount)")
        let channelData = snapshot.value as! Dictionary<String, AnyObject>
        let id = snapshot.key
        if let name = channelData["name"] as! String!, name.characters.count > 0 {
            self.channels.append(Channel(id: id, name: name))
            self.tableView.reloadData()
        } else {
            print("Error! Could not decode channel data")
        }
    })
}

这个密码怎么了？这是来自ObserveSingleEvent的快照的打印：

Snap (channels) {
    "-Ke3g8tLH9A-_iTVjQhq" =     {
        "-Ke3g8tO2XPCbyIjP4Op" =         {
            PictureVersion = "";
            userID = keVlTMUXyRViUsTVjTnKdvZs7mg1;
            username = pietje;
        };
        name = test;
    };
    "-Ke3gFbijlcQGuJXe42L" =     {
        "-Ke3gFbjsEgpA3wjM1Jv" =         {
            PictureVersion = "";
            userID = keVlTMUXyRViUsTVjTnKdvZs7mg1;
            username = pietje;
        };
        name = test2;
    };
}
Error! Could not decode channel data

同样，触发observechannels（）没有显示错误。谢谢您。

最佳答案

你不仅从observe变成了observeSingleEvent，你还从观察.childAdded变成了观察.value。由于您现在正在监听一个.value，这意味着您获得的快照同时包含所有子节点（即使只有一个子节点匹配）。
因此，您需要循环快照的子级以获取之前的通道数据：

func reloadChannels()
{
    channelRef.observeSingleEvent(of: .value, with: { (snapshot) -> Void in
        self.playersInChannnel.append("\(snapshot.childrenCount)")
        for channelSnap in snapshot.children {
            let channelData = (channelSnap as! FIRDataSnapshot).value as! Dictionary<String, AnyObject>
            let id = (channelSnap as! FIRDataSnapshot).key

            if let name = channelData["name"] as! String!, name.characters.count > 0 {
                self.channels.append(Channel(id: id, name: name))
                self.tableView.reloadData()
            } else {
                print("Error! Could not decode channel data")
            }
        }
    })
}

有关如何循环快照的子级的详细信息，请参见此问题的答案：Iterate over snapshot children in Swift (Firebase)

关于swift - 在Firebase中将观察转换为observeSingleEvent时出错，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/42508816/